Passband

The passage area is that the frequency range of a frequency filter in which this can happen, the frequencies contained in an electrical signal. As the limit of the passband typically has an attenuation of 3 dB and the decrease of the signal level is defined to about 71%.

• Low Pass: The frequency range extends from 0 Hz up to the cutoff frequency ft.
• High Pass: The passband starts at its maximum frequency fh and extends upwardly theoretically up to infinitely high frequencies.
• Bandpass: The passband is between the lower limit frequency f1 and the upper limit frequency f2 and bandwidth is, as the filter, a frequency band width f2 - f1 can pass.
• Barrier filter ( notch filter) or band-stop filter: Besides the cut-off frequency and the cut-off frequency range to pass all other frequencies the filter.

A usual in measurement technology and audio engineering width of the passband is 1/3 octave (a third ); such filters are called third-octave filters. Intermediate frequency filters in the FM receivers, for example, have a pass band from 150 to 250 kHz bandwidth.